Great Plains Gardening

By Edith Koeller

July 2, 2004

How many of you are familiar with flea beetles? These are those tiny insects that disappear quickly when you rustle the leaves of some of your garden plants. Signs of infestation are the "shotholes" in the foliage. The beetles in my garden this year attacked the radishes, broccoli, cabbage and even the nasturtiums as the seedlings emerged. Repeated dusting with diatomaceous earth or garden dusting powder containing Sevin and permethrin will control these little pests.

There are several common flea beetles found in Colorado. The western cabbage flea beetle is the most damaging species in the state. Two and occasionally three generations are typical which feed on the cabbage family plants. The pale striped flea beetle feeds on many plants including squash, beans, corn, sunflowers, lettuce, potatoes and many weeds, while the potato flea beetle prefers tomato, potato and other nightshade family plants. Another potato lover is the tuber flea beetle. The larvae of which are associated with tuber injuries. The horseradish, sumac and willow flea beetles are named for the plants on which they feed. The apple flea beetle attack primrose primarily but crabapple and grape are occasionally damaged. Eggplant and some other nightshade family plants are hosts to the tobacco flea beetle, which is more common in the warmer areas of the state.

CSU Fact sheet #5.592 has this to say about these common pests. "Adult beetles, which produce most plant injuries, are typically small, often shiny, and have large rear legs that allow them to jump like a flea when disturbed. The adults chew many small holes or pits in the leaves, which make them look as if they have been damaged by fine buckshot. Young plants and seedlings are particularly susceptible. Growth may be seriously retarded and plants even killed. Leaf feeding also damages plant appearance. This can be important among certain ornamentals and for leafy vegetable crops."

"Flea beetles spend the winter in the adult stage, hidden under leaves, dirt clods or in other protected sites. They typically begin to become active during warm days in midspring but may straggle out over several weeks. Many flea beetles are strong fliers and seek out emerging host plants, which they locate by chemical cues the plants produce."

"The adult feed for several weeks. Soon the females intersperse feeding with some egg laying. They lay eggs in soil cracks around the base of the plants. The minute, worm-like larvae then move to feed on small roots and root hairs. With the exception of the tuber flea beetle, an occasional pest of potato tubers, larval feeding is not considered to cause significant plant injury. The larval stage is typically completed in about a month. The insects pupate, and then emerge from the soil as adults. There may be a second generation during the summer and with a few species, a third generation."

"On established plants, 10 to 20 percent or more of the leaf area must be destroyed before there is any effect on yields. Because seedlings are most at risk, use transplants or plant seeds in a well-prepared seedbed to hasten growth and allow plants to overcome injury. In home gardens, try high seeding rates. Thin the plants once they are established. Trap crops work in some situations. Plant a highly favored crop to attract flea beetles away from the main crop. Radish or daikon can protect other seedlings (e.g. broccoli, cabbage, Brussels sprouts) that are more sensitive to western cabbage flea beetle. The trap crop may then be harvested or destroyed after the main crop has established itself sufficiently to outgrow flea beetle injury. It may also be possible to avoid injury by scheduling plantings so that seedlings are emerging during periods of low flea beetle activity."

"Floating row covers or other screening can exclude the beetles during seedling establishment. In isolated plantings, thick mulches may also help reduce the number of flea beetles by interfering with activity of the root and soil stages."

"Garden insecticides containing carbaryl and permethrin can provide fairly good control for about a week. However, to protect seedlings, applications usually must be reapplied. The plants produce continuous new growth and the highly mobile beetles may rapidly reinvade plantings. As with all pesticides, carefully read and follow all label directions. Pay particular attention to ensure that any flea beetle insecticides being considered are properly registered for use on the crop. Diatomaceous earth is one of the more effective repellents, applied as a dry powder to the plants. Horticultural oils and some neem insecticides also have some repellent effect on this insect."

Until next time…